Machine telephone switching system.



J. N. WALLACE,

MACHINE TELEPHONE SWITCHING SYSTEM.

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MACHINE IELEPHONE SWITCHING SYSTEM.

APPLICATION FILED )UNE 28, 1913.

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MACHINE TELEPHONE swlTcHlNG SYSYEM.

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APPLICATION FILED )UNE 28, 1913. 1,186,051 Patented June 6, 1916.

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UNITED STATES rafrnnfr oFFicn.

-J'OHN N. WALLACE, OF ANTWERP, BELGIUM, .ASSIGrNOR, I EY MESNE ASSIGNMENTS. 'I0 WESTERN ELECTRIC COMPANY,` INCORPORATED, A CORPORATION OF NEW YORK.

f Specification of Letters Patent.

MACHINE TELEPHONE SWITCHING SYSTEM.

PatentedJune o, 1cm.

Application led Juize 28, 1913. Serial No. 776,251.

To all whom it may concern Be it known that I, JonN N. WALLACE, a subject of the King ofGreat Britain, residing at Antwerp, in the Province of Antwerp and Kingdom of Belgium, (whose post- .oilice address is 18 Rue Boudewyns, A-nt- .werp, Belgiuim) have invented a certain new and useful Improvement in Machine 'Telephone Switching Systems, of which the following-is a full, clear, concise, and exact description.

This invention relates to improvements in telephone .exchange systems for the interconnection of telephone lines, and has to do more particularly with systems in which the extension of the desired connection from a calling line to a called line is accom lished vby automatic selector switches under t e control of a'n operator at the central or switching station. Many of the features to be described, however, are not restrictedv to systems of this character, being also applicable, as will be apparent to' those skilled in the art, to systems of widely varying character, as, for example, to full automatic or ina-- chine telephone exchange systems and, particularly'those features relating to the connection of a calling line with an operator, to manual telephone exchange systems One of the principal features of the invention relates to the use in a telephone exchange system' of alternating current, as well as direct current, for both controlling the establishmeuty ottconnectionand the restoration to normal of the automatic selector switches over which the desired connection is established. A

A further feature involvesthe use in such control of both' relays responding only 'to alternating current, and relays responding to direct current; such relays being used where necessary side by side throughout the system, each ).erorniing its proper function in the control of the connection established or being established.

Another"important feature of the invcn tion relates particularly to that construe tion of the system herein disclosed, wherein a connection may bo cstahlislualover a 'plurulity ol' twowoxuluctur trunk circuits. A

Vfurther dcvclopnuul ol' (his feature involves the establishment of a, connection over a piuv rality of such two-conductor trunk circuit@y in series and in succession.

A stillfurther feature of the invention re 52S lating to two-conductor trunk circuits involves the establishment of a connection m er two-conductor trunk circuits in both direc tions from the ofiice or central station at which ther control and, if desirable, super C i vision of the connection is exercised. '.l`h .lr to say, that the connection established .from an ofiice or sub-office to the central or switchlng station at which the control of the selcc tor-switches operating to select, test, rin and seize a desired line is exercised may las over two-conductor trunk circuits, and als the trunk circuits leading from such otlicf at which the control is exercised to a second office, or even to a third oilice, may be o? the two-conductor type.

A still further feature of the invention rc lates to imp rovcd and novel methods and means whereby a successful call may be charged or registered against the c subscriber and involves in part the loi .t f of the apparatus whereby thc charging ru cuit is prepared and controlled in assmifrv tion with the first group selector.

A further feature relating to the re; ing or charging of a call has to do with suon an arrangement of the system that no appa ratus at the final selector or line switch anyof thegroup selectors subsequent to this er to first groupselector is necessary to insure e5 fore referred 'to as controlling the charg i of a successful call` may be located.

.qtlll another fcaturc of the "invention Je lates to an improved, novel and clcicn t failli rangement and constriuiion oi' in a tlaphone exchange syst-rui. Act:

to this feature each central station may have associated therewith one or more sub-central stations or satellites located at a distance therefrom, such satellites being of an improved and novel construction and arrangement of such character that incoming calls may bepromptly and efficientlyreceived and outgoing calls accurately and properly completed. i

A further feature of the invention relates more particularly to the -satell itc in which a called line is selected and involves the immediate restoration of the apparatus at such satellite andthe freeing of the trunk line leading thereto in case the called line is busy.

Another feature of the invention relates more l'iarticularly to systems in which the establishment of' a connection is controlled by what known as the revertive impulse system of control. that is, in which the selecting operations are controlled and ac` con'ipanied by impulses established in the selecting or fundamental circuit by the. movement of a part of the selector, which impulses affect the sending or controlling apparatus under the control of a subscriber or operator until the proper number of im- Y pulses have been sent and the proper selection has been accomplished, when the controlling apparatus will in turn so affect the selector under control that it will stop with the proper selection made. In systems of this character, of which, for example, one is shown inithe Britishpatent specification No. 21260 of 1911 the impulses, instead of passing from the controlling apparatus to the selector under control, pass from the selector' under control to the controlling appdlatdS.

A feature of the invention, therefore, re-

lates to circuits and arrangenmnts ofv apparatus whereby in a selecting or funda.- mental circuit these revertive impulses produced in one portion of the circuit will be reproduced in another and separate portion of the circuit to affect the sending or controlling apparatus.

A further feature of the invention rclating to systems in which a connection is adapted to be established over a plurality of automatically operating switches involves the use of a single test relay or set of test relays arranged to serve a plurality of such switches. More particularly this feature of the invention relates to systems in which a connecting circuit at a central station has associated therewith at each of its ends an automatic switch designed to test for and make contact with one line of a plurality of lines and resides in the arrangement whereby the same relays serve to perform the testing and seizing functions in connection with the operation of both of such automatic switches.

A still further feature of the invention involves the use of a clear, unobstructed registering' con-trol circuit from the first group selector to the called subscribers substation, such circuit having associated ,therewith no bridges conductive to direct current, andsuch bridges as are associated therewith being'without function with regard to the registering operation.

A further feature of the invention relates tothe provision of positive means whereby, in case the line called and selected is busy, the charging'or registering of a call to the calling subscriber will be prevented, such means being located at the first group selector, and being responsive to means located at the final or'line selector operating under the control of' the testing means at such filial selector.

An additional feature of the invention involves the arrangement of circuits and apparatus whereby, upon the attempted establishment of the call and the finding of the line desired busy, all the selectors involved in such attempted connection will, except the first group selector, be immediately restored to their normal conditionand prepared for use in connection with some other call. v This feature of the invention also involves the simultaneous restoration of such selectors after an attempted connection to a busy line, and, further. thel simultaneous restoration of all the selectorsl upon disconnection after a successful call. whereby the time in which any selector is necessarily out of actual ser\;ice is reduced to a minimum.

A still further feature of the invention relates to the location of the busy back apparatus, that is, the apparatus whereby the subscriber, or the operator supervising the connection, or both such subscriber and operator, will be informed that the desired line is busy at the apparatus associated with the first group selector. This feature involves, in addition, the construction wherein the busy back apparatus, although initially controlled by the testing apparatus at the final selector, operates thereafter independently of such apparatus and the connection. in so far as all apparatus subse- 'qucnt to the first group selector is concerned, may be immediately restored to its normal condition.

Another feature of the invention relating particularly to systems in which each calling line is immediately made manifest before an operator by a visual signal and such 4calling lines are automatically connectible one at a time to an operator when idle, involves means whereby such signal will indicate not onlyA the existenceof the call, but also whether or not the calling line to which it is individual is connected to an operator. This result is obtained in the invention herein disclosed by having a calling lamp burn steadily upon the receipt of the call until the line .with which it is individual is connected to an operator, from which time, until the operator is disconnected from such line, the lamp will intermittently flash to indicate such connection.

A still further feature of the invention relates to a new and simplified arrangement associated with a non-numerical switch over which a calling line s connected to a connecting circuit at a central ollice, Where-by a single means exercises various and differeut controls in the dierent stages of the operation.

Another feature of the invention also consist-s in van improved circuit arrangement between a supervising oliicc and a distant oliiec at which the call as extended includes automatic switching apparatus and relates to such an arrangement of the trunk circuit beT tween such ofhces that the control of the automatic switching apparatus may be exer cised thereover in one direction, while the control of a signal at the supervising oflice may be exercised thereover in another d' ection.

Other novel and improved features, particularly such as relater to the controlling apparatus, the control of the finding operation 't the second line finder, that is, the line linder at the controlling' station, the connection of an incoming call to an operators telephoncset, the connection of a cord circuit ltaken for use to an idle controlling equipment of a selected operator, and other features, will suliiciently appear,.from the detailed description'hereinafter given.

'l'here shownone form of the invention, hut it will be understood that the invention is not limited to the particular form or sys tem shown, and is so shown merely for convenience, and is applicable to systems widely varying in character.

The. drawings which comprise 9 figures aset forth diagrammatically a system embodying the invention.

Figure l shows that apparatus involved in the connection located at the first or incoming satellite or sub-central station. Figs, L- and 2a show the connecting circuit and associated appxiratns, including a line finder und a lirst group` selector, situated at the controlling central oilice or station. Fig. 3 shows a second group selector and the apparams assfmiatcd therewith which is also situated at the controlliimr central otlice or Station. Fig. 4 shows a third group selector and its associated apparatus including the relays whereby the controllingr impulses involved in tens and units selection at the linal selector are repeated back to the controlling -alnniratus at the (':ontrolling central ollire or station. all of which apparatus is located at a secoluil central. olliec or station. Fig. 5 shows lthe apparatus involved in the con nection including a conncctin;t4 or line se `morennmt from or set oi terminals to iur lector andA its associated apparatuslocated at a second satellite. Fig. 6 showsfnrther means associated with the connecting circuits at the controlling central oliice or Station whereby the selection and seizing of an operator-s equipment is controlled. Fig. 7 shows apparatus also at the' controlling central office or station associated with, the different operators positions to which the calls coming in on the connecting circuit shown in Fig. 2 are connectible. Figs. 8 and 8 illustrate the two register-controlling equi ments of one of the operators, that is, tllie home operator, showing the such operatorA in full and indicating Sullicient of the B register of such operator to make clear the operation thereof. These figures also show the counting relay a paratus of such A register. Figs. 9 an 9 illustrate the registers themselves of the A register apparatus and the set of manually operable keys by which the controlling operation is controlled by the operator.

The figures should be placed as follows Figs. l, 2, 2, 3, 4 and 5 in order from left to right; Fig. 6 under Figs. 2 and 2a; Fig. 7 under Fig. 6; and Figs. 8, 8a, 9, 9Av to the lcit of Figs. 6 and 7 and in order from left to right.

A connecting or final selector switch such as is diagran'nnatically shown in Fig. 5 is illustrated in British Patent No. 16,867 of lllll. The apparatus associated with this -switch shown in Fig. 5 is somewhat different, but the structure of the Switch will sulliciently appear from such patent and need nrt be herein described. The group .selectors shown in Figs. 2, and 4 are in structure substantially the same as that shown in Fig. 5 and in the British patent referred to. The only substantial difference in the` structure of `the switches from that shown in thc patent is in the brush carriage interruptor devices indicated above the brushes in the several ligures. That is to say, instead of the brush carriage interrupter involving two switch devices as in the British patent and Fig. 5 herein, it in volves a single switch device which 1s closed each time the brush carriage moves from one stage to the next, and is open only when the. brush carriage rests with its released brushes centered upon a set of contacts.

(lf course, in the normal position the inierruptcr brush rests upon the insulated seg ments 270, 371, and 471 of the several se lector switches and as it moves from normal position into position in which the released brushes will make contact and be centered upon the first .set of contacts of Hic row to which they are individual` thc l'nushes Q54, :25h lo! will bo connected to earth over the toothed segment mul then opened as the brushes :uv wonend. ln every suene A register of next this circuit to earth will he again closed and opened as the brushes are centered upon the terminals.

'l`hc line linder switches shown in Fig. 1. and to the left in Fig. 2, are of a somewhat similar construction to that of the selector switches above referred to and shown in liritish latent No. 16867 ot' 1911 hereiiibefore mentioned. yThey are fully described in` lritish patent application No. 16151 of 1912. and will not be herein further described.

The sequence switches which are used throughout thc system shown to control the circuits of the Various portions of the apparatus. and which are indicated ai. 100, 20o, aou. 40o, 50o, Goo, 70o. 75o. soo and S50, are of the type shown in British Patent No. 20810 of 1905). and since they are siilliciently shown and described therein will not be further described. i

Throughout the drawings the sequence switch springs are not indicated in their structural relation to the moving parts of the switch, but are so located as to make most clear the circuits of the system disclosed herein. The positions in which such sequence springs are closed to the contacts shown associated therewith are indicated by the numbers shown adjacent to such springs, such springs being closed to the contact, shown on the saine side of the spring with any given number or numbers. in the position indicated by such numbers. The controlling springs of the respective sequence switches indicated at 101` 201. 301. 101. 501. $01, T01, T51, S01. S51 are the springs which insure that the sequence switch when started from any position will be positively driven into its next stopping position. 'lhe numbers placed adjacent to these springs indicatey they positions in which the springs are open, these springs being closed at all other tinies and positions. 'hei'e these numbers are separated by a minus sign it indi- (fates that the circuit is at all times open between the position indicated by the numbers and is closed only in such positions. whereas where such numbers are separated by the plus sign it indicates that the circuit is closed Continuously between and in the positions indicatcd,--for example. the sequence switch spring 111 top is closed in position 21 and in position but is not closed in any other position nor between positions 3 and S, whereas sequence switch contact 11() bottom is closed iii positions 2 and 1S and continuously while the sequence. switch is passing from position 2 to position 1S..

The set ot' counting relays shown in Fig. S is ot' somewhat similar arrangement to that shown in British Patent No. 255505 ot 1911. Although the circuits are somewhat different from the circuits shown in the patent application referred to, the operation of the set of counting relays is directly analogous to the operation of the set of counting relays in such specitication. In detail the arrangement of the circuit t' the set of counting relays shown herein will sutliciently appear from the detailed description of the operation of the system.

The registers shown in Fig. fr) are structurally precisely like the sequence switches above referred to and shown in the British Patent No. 20811() of 1909. The only difterence in their operation is that they have no normal position, and having been used in connection with one call. remain iii such set position. until used in connection with somo other call.

The n'ianually operable keys shown in Fig. J are arranged in a somewhat similar manner to the keys ot' the ordinary adding machine; when a key is depressed it is held in such position by the energization of a locking magnet individual to the row of which such key forms a part. A key device of this character is disclosed in British patent application No. 23508 of 1911.

Description of opera-imi.-'l`lie System is best described by the description of the. establishnient of a call. and the subsequent restoration to normal ot the` apparatus involved therein. Assuming therefore that a subscriber at the substation 199 desires connection with the .subscriber at the substation 599, the number of which latter substation we will assume to be 1704212, he removes his receiver from its switch-hook. thereby Closing iii the usual manner the circuit through his substation and energizing the line relay 116: the attractioi. of the armature of the line relay closes pilot relay 117 for the group of line finder switches having access to the callingline, and at the saine time. by the arrangciiwnt of such circuit, including the resistances 1111, and 142. places a selectable potential upon the terminal 121 individual to such calling line.

'lhe energization of the relay 117 has closed a circuit through the springs 103 and lillV for the power magnet for each of the idle finders of the gmup controlled by such relay. The brush ca rriages of such idle. line liialers thereupon start in motion and the brushes` 122` 122i. 127i, 125 sweep over the contacts 115. 119.'. 120, 121 ot the various lines connected thereto. which contacts appear in multiple upon each of this group of line iinder switches. .So long as the brushes 123 of the line finders pass over contacts 121 of any non-calling lines. that is to say. over contacts on which there exists no selectable potential as above. referred to. the line find ers continue in motion. As soon. however. as the brush 125 of the line linder reaches the contact 121 upon which such selectable. pi tei'itial exists, the test relay 126 is energized,

a circuit and energizes the and by closing the parallel circuit through' lay the circuit of the power magnet 150 is oi'icned at its back contact, the circuit of the holding magnet 151 is closed at its vfront contact; the brush carriage of the finder switch will therefore come positively to rest Jwith its brushes centered upon the terminals of the calling line. The same operation of the test relay 127 has closed a circuit over spring 113 top to drive the sequence switch V100 out of its first or normal position into its third position. On coming into its second position the sequence switch closes the spring 110, and the circuit is therefore established to energize the cut-off relay 129 of the ca lling line. This in the usual manner cuts oli' the line relay, and ground and battery from such line, and causes the consequent decnergization of such line relay 116 and of the pilot relay 117.

ln consequence of the denergization of the pilot relay 117, all of the line finders which are in motion 'will be brought to a stop. Of course, it tome other call had, meanwhile been initiated the denergization of the line relay 116 would not have caused the denergizati on of the pilot relay 117, and the idle line finders would have continued in motion so long as a line remained unseized upon which a call had been initiated. The circuit for the cut-off relay over the spring 110 is maintained until the restoration of' all the apparatus at this satellite. liorf-f'or'e, as the sequence switch leaves its .ax-ond position the spring 109 may be opened and the test-guard heretofore established on the terminal 121 may be removed. This liar, however. will not be selected by any other line finder as its selectable potential has also been removed by thedencrgization of'the line relay 116 individual to the line. Before, however, the spring 109 is opened the control of the relay 127 is transferred to the callingr subscriber by the flosure of the springs 111 top and 112 bottom. The circuit 'for this` relay will be nmintained through the sixth position of the sequence .switch so long as the subscribers ifwoprirrut is closed at his substation. This for the purpose that should the subscriber hang up his receiver before the call has been extended to the controlling central office, the

d energization of therela 127 will, by driving the sequence switch t rough its seventh' position over the spring. 113, produce the restoration of the apparatus at the satellite.

. `On coming into position 3 the sequence 7 switch 100 closes the sprin 107. Thls initiates the operation of the ine finder apparatus at the, central station to which theA trunk line terminating in the terminals 233,-

234'is connected precisely as did the removal of the subscribers receiver from his switchhook hereinbefore described initiate the operation of the line finders at the satellite. The line relay 231 is energized, energizing the pilot relay 232 and placing a selectable potential upon theterminal 236, such select-4 able potential being produced and adiusted by the resistances 291 and 292. In response to the energization of the pilot relay 232 all the idle line finders of the group having access to the trunk line upon which the call exists will be started in motion over circuits including the springs 209 top, 210 top individual to themrespectively.

As the line finders'move the brushes 237, 238, 239 and 240 thereof will sweepvover the terminals' 233, 234, 235 and 236 individual to the respective trunks appearing in lsuch line finders. When a line finder reaches the trunk upon which the call exists its test relay 241 will be energized and, in the well-known manner, place the test guard upon the terminal 236 ofthe trunk line. The brush carriage, however, will continue to move until the circuit `through the interrupter 243 is opened, when the test relay 242 will be energized, opening the circuit to the power magnet 250, closed over the spring 209 top, and closing the circuit to the holding magnet 251 over the Spring 208 top. The finder therefore stops with its brushes accurately centered upon the terminals of the trunk line upon which the callv exists. The same operation of the relay 242 drives the sequence switch 200 out of its first and normal position into its fifth position by means 0f a circuit over springs 208 top and 203 top. As the sequence switch comes into its second position the circuit is closed over the'spring 226 for the cut-ofil relay 241V and the line relay 231 and the pilot relay 2:32 will bo denergized precisely as the line. relay and pilot relay at the satellite hereinbefore described.

As the sequence switch moves through its third and fourth position, alternating current, the source of which is indicated here and elsewhere on the drawings by a circle including plus and minus signs, ,is applied to the trunk line by the closure of the spring 225 top and a corresponding ground connection is connected to the trunk line to complete the circuit for said alternating current over spring 221 top. This energizes thealternating current relay 132 at the satellite, the current. passing through .the condenser 134. This alternating current, while it is capable of passing through the condenser' 134 as shown, is of sufficiently low frequency and has such other electrical characteristics that itv v'ill be inaudible and unobjectionablc to the calling subscriber if by chance it should be impressed upon the circuit leading to his receiver.

The energization ot' the relay 132 at the satellite. by ineans of a circuit includingr the springs 114 top and 105 top drives the sequence switch '10() into its 7th position. As this sequence. switch comes into its 6th position` the alternating current circuit being by this time open at the sp1-ings 224 and 225 at the central oflice, it closes a substitute circuit for the relay 12T through thev spring 111 bottom. armature and back contact of thevrcla y 132, Spring 106,v front Contact and armature of the relay 127 and spring 101 bottom so that thc restoration of the apparatus at the satellite still controlled by the relay 127 now awaits the energization of the relay 132. i

` Position 7 in which the sequence switch 100 comes to rest is the through or talking position ol such sequence switch,I and in such position the calling subscribers line is connected through to terminals '233, 234 of thev second line lln'der switch located at the central or controlling station.

' Then the connecting circuit sequence.

switch Q00 comes into its 5th position the. circuit of the calling subscriber is connected through to the repeating coil 216 and current is supplied to such subscribers circuit from the battery included between the Windings thereof. The supervisory lamp 263 will not bc lighted at this time, although the.

spring 223 is closed, because the supervisory relay 217 is energized. However` the calling lamp Qtwvill be lighted due to the closure in this position of the spring 207 top. r1`his will indicate to the operator that a call is waiting upon the connecting circuit to which such calling lamp is individual. It the operator in whose position the connecting circuit, shown in Fig. 2 is situated is idle at this time such connecting circuit will be immediately and automatically connected to such operator`s telephone ,equipment and to an idle controlling equipof such sequence switch.` The sequence switch 600 therefore moves into its second position. This is the testing position of this distributing sequence switch. In thisposition battery connected to' the high resistance winding of thc rclay 686 individual to the home operator of the position in which the connecting circuit shown on Fig. 2 appears such relay being also individual to this particular connecting circuit. At the saine time the battery is connected to the correspond ing winding of the relay 6517 appropriated to that connecting circuit but which is individual to an alternate or helping-out opera tor, such operator being, for example, the operator whose position is immediately to the left ofithe home operator. It will be understood. of course, that an additional helping-oiit or alternate operator may be provided in the person ot' the operator to the right of the home operator, but for clearness and siiniiilicity the apparatus of but a single helping-oiit operator isshown. Battery connections referred to are provided by the springs o. (307. If the home operatoris busy. her sequence switch 700 will be out of its normal position and no circuit will be established for the relay (33o. lf the alternate operator is busy, her scqiience switch 750 will be out of its normal position, or if, even though she is idle, her helping-out key 771 is not thrown` no circuit will be provided for the relay 637. So long as neither of these relays (336 and 637 is energized the distributing sequence switch 600 will remain in its second position. Immediately. however, that the home operator becomes idle. or the alternate operator 4is idle and her helping-out key 771 is closed,

the relay 636 or 637 appropriated to such operator will be energized and the operation oi selecting an operator and an equipment of such operator will begin.

mtwwill be understood vthat i'or each Connecting circuit of a position there will be a relay 636 ofthe home operator, the high rcsistance winding of which is connected to the ci'mdnctor leading to the top contact of the spring 703. all of such higlrresistancc windings being connected in parallel to such conductor. Similarly for cach connecting circuit of u position there wil' lic a relay Gili' ot' the alternate operator, the high resistancf` windings of which are connected in parallel to the conductor leading to the contact of the lielping-oiit key 771. It may be. therefore. that a plurality of connecting equipment of such operator. linmediately.' that the circuit through the high resistanc-i'` `winding of'tlic relay G36 is closed at` the .circuits are. simultaneously attempting. to select and seize an idle operator and an idle switches 600 of which are in second posi- Vbut the currentr in the parallel branches through the low resistance windings ofthe -relays 636 will not be sufficient to energize two vof 'such relays simultaneously. Thercvfore,when the circuit through the high resistance windings is open at theI back contact of relay 716, as it is energized to drive the home operators sequence switch 700 into second position, the relays G36 connected in parallel willv allow their armatures to retract until circuit is closed through but one of them, which will be the one the armature of which would be the last to open thc eircuit at its front Contact. This relay 636 alone will remain energized. Therefore, when the sequence switch 7 00 comes into its second position but one of the relays 636 is or remains energized. ln this position a shunt is closed around the high resistance 739 through the spring 705 bottom,'so that sufiicient current will pass through the relay (338 to energize it and the sequence switch (S00 will move out of its second position and under the control of the relay 636 and the spring 605 move into its eighth position.

This operation by which the home operator is selected rather than the alternate operator will take place if the home operator is idle. whether or not the alternate operator is busy or idle. lf the alternate operator is busy obviously no circuit will be provided for the relay (337. Ii the alternate operator is idle and her helping-out key 771 is closed, the relay 637 will be energized and the alternate operatoi"s sequence switch will have moved. but as the distributing sequence switch 6U() will be driven through its position individual to the alternatcoperator, no 'circuit will be established to hohl the, alternate operatol"s sequence switch 750 in its fifth position. and such sequence switch will immediately return to its normal position. It'. however. the home operator is busy. the alternate operator observing thc calling lamp 245 to be lighted may close her yhelping f-out key 77l (unless it is already closed) and if such operator is idle the same selecting operation will take place with re gard to the alternateoperator as has been described with regard to the home operator. In this case, however. the distributing sequence switch 600 will only be driven into its third position by the energization of the 'relay 637 and the closure of the spring 604, top. From position 3 when the alternate operator has been seizedthe operation of seizing an idle register of the alternate operator will take place precisely as will the seizure of an idle registering equipment of the home operator with the distributing sequence switch 600 in the eighth position.

For the purpose ot' illustration, therefore,

it will be assumed that the home operator is idle and the distributing sequence switch 600 has moved into its eighth position. As the sequence switch 600 comes into its eighth or tenth position, the relay (338 being deenergized. it establishes a circuit over the springs (318 and 202 bottom, to drive the se quenee switch 200 into its sixth position. In the sixth position of thel sequence switch 200 and the third, sixth, eighth or tenth positions of the sequence switch t100, the calling lamp '245 depends for current on the circuit through the interi-opter G2G and the spring (i033 bottom. This will cause the lamp to flash. indicating that the connecting circuit to which it is individual is the onewhich is now connected to an operatol"s equipment.

lpon the opening ol' the circuit ofthe relay 716 at the spring (305 top, this relay is deiinergized and the home operators sequcnce switch 7U() driven from its second position. .\s this sequence switch comes into ils l'ourth position. the circuit is again established lor this rela)v over springs 7l() top` 71H. (Sos top and 212 bottom. This will 95 energize the relay 71o again before the sequence switch 70H reaches its lifth position, and this sequence switch will therefore stop in such position. ll when the, sequence switch not) comes into its eighth position the register olI the home operator is idle, the relalv UBS will he energized over springs Go2. haelt contact ol' relay G39. springs 20G, tilt) bottom. 7013.870, H03 bottom and back contact and armature of the relay 825 of the register equipment. This circuit will energizey the relay (338 in the eighth and' ninth positions ot thel sequence switch and such sequence switch will therefore beA driven into its tenth position which with 11o the eleventh position are the positions individual to the A register equipment of the home operator on such sequence switch. It will be observed that this circuit depends on the closure of the spring-2.06, indicating thereby that the connecting circuit is ready to have the connection extended, that it depends on the s )ringi706 indicating that the home operators telephone set is connected to the seizing connecting circuit, that it decates that the B register equipment is no longer using the set of manually operable keys shown in Fig. 9, which are common to the A and B` register equipments of the home operator';"and finally that it depends upon the spring 803 and the armature of the 186 'sitio-n and into its second position.

ixday 8 which together indicate that the register equipment is idle.

lli the A register equipment had been busy the` eil-nuittraoed would ha ve been open at the springK 803. 0n the other hand. a cireuit would have been established over .the maior portion of suoli eireuit and through the, spring 855i top and the high resistance relai; i' oi' the B register eiiiiipiiwlxt. In the erent. that the A register mguipment is idle the relay ST5 would here been shunted and eould not have been euern'iz'rd. lf the A, register equipment is husy the. relay ST5 would have been energized. but insuiiieient rurrent would hay@ passed therethroluljh to energire the relay 63S, and therefore ilthonggfh the B register equipment would h ave been seixed and its apparatus started in operation, the seuueuee switch t300 would have remained in the eighth position. On the.

other hand. assuming the register equipment to he idle. immediately that the quenee switch 300 comes into its tenth posi tion a eireuit, will be established for the h ign resistance relay if!) over the cireuit traced before to the spring G10, but now over the top contact. of such spring. spring'ti. spring;` S05 top and relay 825i. When thi?J circuit is established, the relay S25 energized. but insuliieient current pass therethrough to energize the relay G38 Ythe sequence switch 000 will remain in its tent-5i position. Since the energization of th:x .relay ST5 ot the B register equipment in the eighth position of the sequence swittfh t300 is followed by the :same operations as the energ'ization of the relay' of the A register equipn'ient in the tenth position ol the sequence switrh t100. a description of sueh subsequent operations in connection with one of the register equipments will sutiice. It will therefore be, assumed that the A register ol the home operator is. idle, and that therefore the seipienee switch 600 is in its tenth position and the relay 8:25 is energized. The energization of this relay 825 drives the register equip ment sequence switeh S00 out ol' its first po- This movement immediately opens the circuit. of such relay S23, and by its denergization it drives the. sequenee switch S0() out ot' its seeond position. and such sequence .switch nuder control of its springr S01 will more into its fourth posi tion. As this sequence switeln however. comes into its third position. a ci rouit' closed for the relay over the Spring G17 top and I y bottom, so that heffgre the sequeneeswiteh 800 com` into its fourth position this relay energiLed and the sequence switeh will stop inits 'fourth position.

'hen the seguirne@.switch 000 tomes to rest in'eithei itsy tenth position. as deseritn-d or in its eighth position the'ii register the alternate operator has been Seized) a rirruir is established over the springs 018 and 20;! bottoni to drive the Sequenceswitch 200 into its sixth v1 .;1sition. At this time. the springs 009 top and Gil bottom' are closed and also in the sixth position of the sequence switrh 00 the spri 120 top and 219 bottom are rlosed. A mruuit is therefore established for the home niwratois telephone set .'19 to (he rounertinn4 eirouit over the oon-- duetors fr'. c (broken in Fig. 2 for elearness) so that the operator may converse with the railing subscriber and impure and learn the number oi' the desired line. lhen the operator has thus learned the number ol' the lin(` wantel. .she will depress the manually operable keys shown in Fig. 9 to indicate sufh number thereon in a well understood manner.

In the fourth position of the register sequenee switiih *00* the apparatus is ready for the operator to indicate the mnnber of the. desired line upon the manually operable keys. shown in Fig. 9, by depressing the appropriate key of each of the groups 0f ,ligit keys. The preparation of these eircuits and apparatus for sueh actby the operator has. ol' eourse. taken place while the operator has been learning.;- from the subscriber the number ot the. desired line. ll'e have assumed that the number of sueh line is 170492. The operator will therefore depress the number l or second key of the row to the extreme right of the set ot inanually operable keys; the number T or eighth key of the next row ot' keys; the number 0 or h'rst key of the next or 1000s row of keys; the number et or fifth key of the next or l00s row ot keys; the number 9 or tenth key of the next or 10`gs row of keys, and the number i). or third key of the last or units row of keys. llaeh key as it is depressed will be locked and held in sueh position by the lockingmagnets indicated for the several rows of keys. the energizing circuit for whieh is elosed by the spring 81.4 in the fourth and fifth positions of the sequence switeh S00. lt. is assumed that the keys vwill be depressed in order either 'from the highest digit to the, lowest or from the lowest digit to the highest. 'hen, theretore. all the keys are depressed' a circuit will be closed through the depressed units key and the depressed '100.000s key, to start the various registers 901, 902, 903, 904, 905, 906 in motion over the spring 809 and also a circuit `for the relay T18 to drive the operator`s sequence switch out of its' fifth position. The operator having learned the numher desired. and indieated such number upon thenrannally imei-able keys, her attention is no longer required. and her telephone therefore need no longer he. connected to the 

